The invention relates to a colour display tube comprising an envelope having a substantially rectangular display window and a substantially rectangular colour selection electrode which has a large number of apertures. The color selection electrode is suspended from supporting elements each connected in a corner of the display window by means of suspension means comprising a flat resilient element connected to the colour selection electrode. Each flat resilient element extends substantially perpendicularly to the electron beams deflected towards the respective corner. Each supporting element cooperates with a flat resilient element of the suspension means by means of a stud connected to one of the cooperating elements, said stud extending partly through an aperture provided in the other cooperating element.
Such a colour display tube is described in prior non-prepublished Netherlands Patent Application Nos. 8004173 corresponding to U.S. Pat. No. 4,387,321; and 8004174 corresponding to U.S. Pat. No. 4,358,702.
In the suspension described in Patent Application No. 8004173 the supporting element is formed by a pin which is sealed in the corner of the display window and at the free end of which the stud is present. The axis of the stud is substantially perpendicular to the plane of the flat resilient element. Near the end remote from the colour selection electrode an aperture is provided in the flat resilient element. The colour selection electrode is suspended in the display window by placing the flat resilient elements with their apertures on the studs of the pins. The studs project partly through the apertures. According to a further embodiment, the position of the apertures in the flat resilient elements may be adapted to the position of the studs by providing the flat resilient elements with slot-shaped apertures and placing apertured plates for the studs on the resilient elements. After suspending the colour selection electrode the plates are permanently connected to the flat resilient elements.
In the suspension described in Patent Application No. 8004174 the supporting element connected in the corner of the display window has a flat portion which is substantially perpendicular to the electron beams deflected towards the relevant corner. An aperture is provided in said flat portion. Near the end remote from the colour selection electrode the flat resilient element has a stud the axis of which is perpendicular to the plane of the flat resilient element. The colour selection electrode is suspended in the display window by placing the flat resilient elements with their studs in the apertures of the supporting elements, the studs projecting partly through the apertures. In this suspension also, according to a further embodiment, the position of the studs may be adapted to the position of the apertures by providing the studs on loose plates, which plates are permanently secured to the flat resilient elements after suspending the colour selection electrode.
In both above-mentioned Patent Applications the flat resilient element fulfils three functions. First, the flat resilient element causes the colour selection electrode to move in a direction towards the window in the case of expansion. When the colour selection electrode expands, a smaller distance is necessary between the colour selection electrode and the display window to maintain a colour pure picture. Since each of the flat resilient elements is substantially perpendicular to the electron beams deflected towards the respective corner, the colour selection electrode moves towards the display window as a result of the spring action of the flat resilient elements. Second, the flat resilient elements fix the position of the colour selection electrode with respect to the display window. Third, the flat resilient elements ensure the maintenance of said position of the colour selection electrode. For this purpose the flat resilient elements exert a certain clamping pressure on the supporting elements so that in the case of vibrations any change in the position of the flat resilient elements changes with respect to the supporting elements. In order to be able to exert a sufficiently large clamping pressure the flat resilient elements should be comparatively thick.
During manufacture, the display tube is heated to approximately 400.degree. C. while adhering the display window to the cone and while evacuating the display tube. During this heating the colour selection electrode expands and, as a result of the deflection of the flat resilient elements, moves towards the display window. It has been found, however, that after cooling the display tube, the flat resilient elements do not always return to their original position, which causes displacements of the colour selection electrode and consequently colour defects in the observed picture.